1. Field of the Invention
The present invention relates to a method of and an apparatus for all make busy detection of a line concentrator, exchange or the like used in a data communications system.
2. Description of the Prior Art
Generally, for a line concentrator or an exchange the function of making all incoming circuits busy when all outgoing circuits are made busy by the problem in a higher ranked unit or circuit disconnection, i.e. the all make busy function is necessary. For this purpose, in the past all the outgoing lines were supervised to detect the time at which all outgoing lines become busy. In this case, however, it is necessary to detect whether or not an outgoing line is in use to separate it.
As a result, even a circuit which seldom operates has the above-described detecting function, so that the circuit becomes complicated and uneconomical. Furthermore, there is the disadvantage that when it is necessary to temporarily interrupt the call for the terminal by, for example, in necessity of the testing the higher ranked unit, all the outgoing circuits of the higher ranked unit must be made busy, requiring a time-consuming operation. The degree of this disadvantage becomes greater as the number of the outgoing circuits of the line concentrator or exchange becomes larger.
To facilitate the operation of the higher ranked equipment it has been a practice that a special signal line is provided between the line concentrator or the exchange and the higher ranked unit for transmitting the signal indicating the trouble in the higher ranked unit. However, this expedient has the disadvantage that it requires an additional circuit and it is necessary to supervise the state of the circuit for detecting the circuit breakage, resulting in the circuit complication.